In recent years, computer printer technology has evolved to a point where very high resolution images can be transferred to various media. One particular type of printing involves the placement of small drops of a fluid ink onto a surface in response to a digital signal. Typically, the fluid ink is placed or jetted onto the surface without physical contact between the printing device and the surface. The specific method for which the ink is deposited onto the printing surface varies from system to system. However, two major methods include continuous ink deposit and drop-on-demand ink deposit.
With regard to continuous printing systems, inks used are typically based on solvents including methyl ethyl ketone and/or ethanol. Essentially, continuous printing systems function as a stream of ink droplets are ejected and directed by a printer nozzle. The ink droplets are directed additionally with the assistance of an electrostatic charging device in close proximity to the nozzle. If the ink is not used on the desired printing surface, the ink is recycled for later use. With regard to drop-on-demand printing systems, the ink-jet inks are typically based upon water and glycols. Essentially, with these systems, ink droplets are propelled from a nozzle by heat or by a pressure wave. Additionally, all of the ink droplets are used to form the printed image and are ejected when needed.
There are several reasons that ink-jet printing has become a popular way of recording images on surfaces, particularly paper. Some of these reasons include low printer noise, capability of high speed recording, multi-color recording, and potential versatility. Additionally, these advantages can be provided at a relatively low price. However, though there has been great improvement in ink-jet printing, accompanying this improvement are increased printing demands, e.g., higher speed, higher resolution, full color image formation, new applications, etc.
Papers used for ink-jet printing have typically included high-quality and wood-free papers designed to have high ink absorptivity or papers having a coated porous surface. These papers are functionally good for ink-jet printing because the inks may be absorbed readily and dry quickly. However, such papers often do not allow for a crisp or sharp image. Additionally, there are many potential substrates that do not provide avenues for absorption, and thus, typical ink-jet inks can puddle on those surfaces. For example, non-porous plastic is such a substrate.
Polyvinyl alcohol-acetate is a commercially available polymer produced by partial hydrolysis of polyvinyl acetate. However, there are various specific structures that can be formed based on several variables. For example, different chain length and degree of hydrolysis can effect the properties of the structure. Specifically, the solubility of polyvinyl(alcohol-acetate) in water is dependent, in part, upon the degree of hydrolysis that the polyvinyl acetate has undergone. To illustrate this, a fully hydrolyzed product is typically soluble only in hot water and tends to have a high degree of crystallinity in the dry state. On the other hand, a polyvinyl(alcohol-acetate) polymer that is about 88% hydrolyzed is water-soluble at room temperature. Non-hydrolyzed polyvinyl acetate is not water-soluble.
Polyvinyl(alcohol-acetate) has been widely used in making photo paper and special papers for ink-jet applications. However, its use as an ink-jet ink component has been very limited. The problems associated with the use of polyvinyl(alcohol-acetate) in ink-jet inks include poor long term and short term nozzle reliability due to increased viscosity and nozzle plugging.
One property of polyvinyl(alcohol-acetate) is that it can be gelled in presence of some chemicals, such as borax, boric acid, or copper sulfate. However, this property has not been known to be used for ink-jet applications. Though the formation of plasticized gels can be desirable when printing on certain types of media, e.g., specialty media including non-porous plastics, the difficulties associated with jetting are problematic.
Thus, it would be desirable to provide compositions and methods for printing on specialty media such that good pen reliability could be maintained, and yet also provide good gelation properties once printed on a substrate.